Like other shrimp farmers here in this lush, canal-lined province in Vietnam’s Mekong Delta, Nguyen Van A can instantly rattle off the precise percentage of saltwater in which crustaceans grow best. And at the moment, he insists with a smile, everybody knows that Ben Tre Province has the best brackish water in the world.

“Shrimp and crabs in Ben Tre are always better than shrimp and crabs elsewhere, because the saltwater percentage is the best, so the meat tastes better,” he said.

But Nguyen Van A also knows the percentage at which they begin to die.

Last year, when the delta was devastated by the worst drought in recorded history, the amount of salt in Ben Tre’s water hit that target, and kept shooting up. The province's rice crops were the first to die, followed by hardier fruit trees and coconut palms. But eventually, even his salt water shrimp were all lost.

“The weather has been unstable for the past two or three years,” he said. “I lost money. It’s like gambling.”

Nguyen Van A is one of millions of people gambling with the impact of climate change in the Mekong Delta.

As sea levels and temperatures rise, rice farmers are losing crops to salt water intrusion. While salinisation could offer more opportunities to switch to shrimp farming, that industry is notorious for destroying mangroves – the tangled forests that grow in brackish water and are key to protecting coastlines from storms, which are increasing in frequency and intensity due to climate change.

About 280 kilometres south of Nguyen Van A’s shrimp farm, in Ca Mau Province, conservationists are teaming up with locals and companies on a project that could provide part of the answer to the climate change conundrum Vietnam and other countries are facing.

The International Union for the Conservation of Nature and the Netherlands Development Agency have launched a programme to incentivise farmers along the coast to preserve the trees by setting up what are known as “shrimp-mangrove systems”. The initial phase of the Mangroves and Markets project enlisted 2,000 families living in two protected mangrove forests that were losing tree cover to aquaculture.

The shrimp farmers promised to maintain at least 50 percent mangrove cover. In exchange, they got help certifying their shrimp as organic, which allows them to sell it internationally at a premium. This more than repays them for the effort of planting and caring for additional trees.

The Mangroves and Markets project has recently begun working with farmers in Ben Tre Province and neighboring Tra Vinh. Andrew Wyatt, a programme manager at IUCN, said there is little point in fighting the salinisation that is destroying rice farming; a better strategy would be to figure out how to work with salt water.

“We need to live with salinity and treat it as an opportunity rather than a threat,” he said.

Sinking delta

It’s often said there are no climate change deniers in Vietnam. The long, skinny country of 95 million people hugs the coast for thousands of kilometres, much of that at low elevations. The Mekong Delta in the country’s south is one of the most fertile areas of the world, an estimated 39,000 square kilometres of loamy, wet soil.

It is also sinking, according to experts, including Duong Van Ni, a professor at Can Tho University who focuses on climate issues.

The subsidence is due to a combination of rising sea levels and erosion, caused by a complex cocktail of factors, including increasing climate volatility, more groundwater extraction and hydroelectric dams being built upstream on the Mekong.

But the effects are clear.

“Because of the impact of both climate change and upstream hydropower dams, environmental disaster happens very often and it pushes poor people to migrate,” he said. “This is happening heavily in the coastal areas of the Mekong Delta.”

The Mekong Delta has long been central to the Vietnamese government’s “Rice First” policy, which encouraged intensive rice cultivation as a means of catching up economically — and feeding its citizens — after decades of war.

The policy achieved these goals, but in the process the fertile delta soil has been depleted. At the same time, rising seas are causing saline intrusion that kills the relatively delicate crop.

Living with saltwater

Wyatt, of the IUCN, argues that a paradigm shift is needed in how saltwater is seen.

Since the reunification of the north and south in 1976, the government has pursued an aggressive water management policy designed to support its rice cultivation targets. This has led to the construction of more and more sluice gates, dams, and dykes to keep freshwater in and saltwater out.

But Wyatt says this is unsustainable. The infrastructure is increasingly ineffective against rising seas, even as the Vietnamese government is taking on more and more debt to build and reinforce it. Opening sluice gates also flushes agrochemicals into coastal areas.

Instead of treating salinity as an enemy, Wyatt says, residents of the Mekong Delta need to learn to embrace it. Counter-intuitively, giving up the fight and letting in the rising seas can even have environmental benefits.

“We also need to keep these ecosystems open instead of sluicing off these rivers,” he said. “Then we have better biodiversity outcomes.”

Farmers are increasingly recognising this: in some areas, they are even demanding that sluice gates be opened and salty water be allowed to flow in so they can begin growing shrimp. But official policy has lagged behind.

Shrimp-mangrove cocktail

Ca Mau, the province at the southernmost tip of Vietnam, is surrounded by ocean on three sides, making it especially vulnerable to rising seas and typhoons. The location also makes it a particularly good place to start a shrimp farm. But shrimp farming could destroy many of the same mangrove forests the province depends on for protection.

Those working on the Mangroves and Markets project hope to change that by switching to shrimp-mangrove systems. “Before the project, around 10 years ago, the trend was for the shrimp to expand and the forest to dwindle,” Wyatt said.

In contrast to large, boxy industrial shrimp farms, shrimp-mangrove systems are long and thin, with brackish pools of water alternating with strips of mangrove trees. In addition to providing a more sustainable way to protect the coast than concrete seawalls, shrimp-mangrove farms actually raise the level of the earth by trapping sediment. In some cases they can accumulate as much as 25 centimetres of earth annually, which is greater than sea level rise and subsidence combined.

Unlike intensive shrimp farms or shrimp grown in rice paddy fields, they also cool themselves, which requires less groundwater pumping and makes them more resilient. During last year’s drought, many mangrove-shrimp systems escaped unscathed even as shrimp on other types of farms died in droves, according to Wyatt.

Mangroves and Markets has been so successful that it is now working with thousands of additional shrimp farmers Ben Tre and Tra Vinh, where mangroves are also under threat and erosion is a major problem – up to 60 metres of shoreline per year are lost in some areas.

This will be good news for farmers along the coast like Nguyen Bin A, who says he knows mangroves are ecologically important, but isn’t quite clear on why.

But there’s one thing he’s sure of: “In the future, if the sea levels rise, it doesn’t matter if you build a dam higher. It will destroy your farm.”